1. Field of the Invention
The present invention relates generally to the field of pipe connections, and in particular, to an improved belling process and apparatus useful therein for installing a gasket in a bell or socket end of a thermoplastic pipe.
2. Description of the Related Art
Pipes formed from thermoplastic materials including polyethylene and PVC are used in a variety of industries. For example, pipes are commonly used in the municipal waterworks industry for the conveyance of fluids such as water and sewage. It is well known in the art to extrude plastic pipes of this type in an elongated cylindrical configuration of a desired diameter and to then cut the extruded product into individual lengths of convenient size suitable for handling, shipping and installing. Each length of pipe is enlarged or “belled” at one end sufficiently to join or connect with the next adjacent pipe section by inserting an unenlarged or “spigot” male end of the next adjacent length of pipe into the enlarged bell pipe end. The inside diameter of the bell is formed sufficiently large to receive the spigot end in telescoping fashion.
Some form of sealing element or composition must be used to form a secure connection between the male and female pipe ends. For this purpose, an annular, elastomeric ring or gasket is typically present within a groove formed in the bell, socket end of the thermoplastic pipe. As the spigot is inserted within the socket, the gasket provides the major seal capacity for the joint. It is critical, during the installation process, that the gasket not be able to twist or flip since a displaced or dislocated gasket will adversely affect the ultimate sealing capacity of the joint.
In some instances in the past, the sealing gasket was installed in the groove of a bell pipe end after the bell end had previously been manufactured with such a groove at the pipe manufacturing facility. In other words, the gasket was installed in a post pipe manufacturing operation. However, in the early 1970's, a new technology was developed by Rieber & Son of Bergen, Norway, referred to in the industry as the “Rieber Joint.” The Rieber system provided an integral sealing mechanism within the belled or female pipe end for sealing with the spigot end of a mating pipe formed from thermoplastic material. In the Rieber process, the elastomeric gasket was inserted within an internal groove in the socket end of the female pipe as the female or belled end was simultaneously being formed. In other words, the gasket was installed simultaneously as a part of the pipe manufacturing operation rather than as a post manufacturing operation. The provision of a prestressed and anchored elastomeric gasket during the belling process at the pipe factory provided an improved socket end for a pipe joint by providing a sealing gasket which would not twist or flip or otherwise allow impurities to enter the sealing zones of the joint. This increased the reliability of the joint and decreased the risk of leaks or possible failure due to abrasion. The Rieber process is described in the following issued United States patents, among others: U.S. Pat. Nos. 4,120,521; 4,061,459; 4,030,872; 3,965,715; 3,929,958; 3,887,992; 3,884,612; and 3,776,682.
In the previously described Rieber process, the gasket is installed upon the outer working surface of a mandrel and abuts a backup collar which helps to position and retain the gasket during the subsequent belling operation. In many cases, it is necessary to heat the collar so that the lip region of the female pipe will not buckle. A cold back up collar accepts heat from the bell lip region. As the lip region cools, there is an increase in the coefficient of friction between the bell lip region and the collar. This increase in friction can cause buckling of the collar as the collar cools and the mandrel is withdrawn. While heated back up collars have been used in the past satisfactorily, the heating aspect of the collar adds to the cost and complexity of the tooling.
Thus, despite the advances in the art as described above, a need continues to exist for further advances in the technology. For example, it would be advantageous to develop a back up collar of the type described which eliminates the need for heat during the pipe belling operation.